Show in DevTools

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered; the description adds genuinely useful context by naming the target panel and the DevTools-open prerequisite that will cause failure. It doesn't say what happens when DevTools is closed (error vs no-op) or whether navigation in the panel replaces current DevTools state.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

One dense sentence with a colon-delimited structure that front-loads the action and then enumerates the two modes, plus a short prerequisite clause. No filler sentences.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a zero-required-parameter mutation-of-UI tool with no output schema, the description covers the modes and the prerequisite well. The notable omission is that nothing says a call with no arguments is invalid/meaningless, which an agent could easily attempt given the empty required list.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the raw parameter meanings are already documented; the description earns extra credit by explaining the combinatorial pairing — ref/selector belong to the Elements mode, url+line to the Sources mode. It does not state that at least one mode's parameters must be supplied, which is the main semantic gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a concrete verb ('Shows') and two well-defined resources/modes: an element in the Elements panel or a source file in the Sources panel, each with the parameters that select it. It's clear what the tool does, though it doesn't explicitly contrast itself with neighbouring inspection tools like dom_inspect or devtools_context.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides the key prerequisite ('Requires DevTools to be open on the tab') and clarifies that the effect is user-visible, but gives no guidance on when to prefer this over dom_inspect, devtools_context, or evaluate for similar inspection goals. Usage is implied by the two modes rather than stated as selection criteria.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.